This invention relates to a method of manufacturing a touch screen panel in which transparent hard coat material is deposited before the edge electrodes and the wire traces so that the hard coat is under the edge electrodes to eliminate the color variation present at the edges of the panel when the transparent hard coat material is deposited over the edge electrodes and wire traces.
Touch screens are now ubiquitous and used as the input and display interface at, for example, automatic teller machines, gambling machines in casinos, cash registers, and the like. Touch screen panels generally comprise an insulative (e.g., glass) substrate and a resistive layer disposed on the insulative substrate. A pattern of conductive edge electrodes are then formed on the edges of the resistive layer. The conductive electrodes form orthogonal electric fields in the X and Y directions across the resistive layer. Contact of a finger or stylus on the active area of the panel then causes the generation of a signal that is representative of the X and Y coordinates of the location of the finger or the stylus with respect to the substrate. In this way, the associated touch panel circuitry connected to the touch panel by wires or wiring traces can ascertain where the touch occurred on the substrate. Typically, a computer program generates an option to the user (e.g., xe2x80x9cpress here for xe2x80x98yesxe2x80x99 and press here for xe2x80x98noxe2x80x99xe2x80x9d) on a monitor underneath the touch screen panel and the conductive edge electrode pattern assists in detecting which option was chosen when the touch panel was used by the user.
In the prior art, a resistive layer (e.g., tin antimony oxide) is sputtered onto a glass substrate. The conductive edge electrodes and wire traces are then deposited on the resistive layer about the periphery of the panel using a thick film paste. A SiO2 transparent hard coating is then applied to the panel over the conductive edge electrodes and wire traces to protect the panel during use.
Because of the thickness of the edge electrodes and wire traces, however, the hard coat is not planar and instead rises up at the edges of the panel causing a cosmetic defect in that color variations are present at the edges of the panel. These unacceptable color variations are a major yield issue of capacitive touch screen panels incorporating SiO2 transparent hard coatings applied by a wet chemical processes when the liquid hard coat material dams and drains around the edge electrodes and wire traces.
Furthermore, cracking and islanding of the thick-film material causes functional failures and is an additional major yield issue in capacitive touch screen manufacturing. This problem is caused by a chemical interaction between the thick-film of the edge electrodes and wire traces and the SiO2 transparent hard coating and by mechanical stress on the thick-film during densification of the SiO2 hard coating network.
If, on the other hand, the SiO2 transparent hard coat material is deposited before the edge electrodes and the wire traces so that the hard coat is under the edge electrodes and wire traces to eliminate the color variation problems, the hard coat material prevents the establishment of the correct electrical connection between the edge electrodes and the wire traces with the resistive coating.
It is therefore an object of this invention to provide a new method of manufacturing a touch screen panel.
It is a further object of this invention to provide such a method which eliminates color variations at the edges of the panel.
It is a further object of this invention to provide such a method which reduces or eliminates functional failures of the touch screen panels which occur due to cracking or islanding of the thick-film of the edge electrodes and wire traces.
It is a further object of this invention to provide such a method which increases the yield in the manufacture of capacitive touch screens.
It is a further object of this invention to provide such a method which eliminates the SiO2 coating over the thick-film conductive material of the edge electrodes and wire traces to thereby minimize the adverse interactive effects associated with the prior art where the SiO2 coating covered the edge electrodes and the wire traces.
It is a further object of this invention to provide such a touch screen panel with an SiO2 hard coat which is more fully densified.
This invention results from the realization that the color variations and the other problems associated with applying an insulative protective coating to touch screen panels over the edge electrodes and wire traces can be overcome by evenly applying the insulative protective coating to the touch screen panel before the edge electrode pattern is deposited thereon and by adding a sodium carbonate or sodium formate composition to the thick film silver/frit paste of the edge electrode and wire trace material so that the edge electrodes etch through the protective coating when the panel is fired to thus properly establish electrical contact with the resistive coating on the panel under the protective coating.
This invention features a method of manufacturing a touch screen panel in which a resistive coating is applied to one surface of an insulative substrate, an insulative protective coating is applied to the resistive coating, a conductive edge electrode pattern including a plurality of edge electrodes is deposited on the protective coating, and the panel is fired until the edge electrodes etch through the protective coating and make electrical contact with the resistive coating.
Preferably, the material of the edge electrodes includes conductive paste mixed with an additive. The insulative protective coating may be or include silicon dioxide and the additive then may include a chemical compound which is converted into a molten alkali hydroxide at elevated temperatures which dissolves the silicon dioxide of the protective coating. Typically, the chemical compound is selected from the group consisting of sodium carbonates and/or sodium formates. Usually, the conductive paste is a silver/frit composition. The additive typically comprises 1-25% by weight of the conductive paste.
The step of applying the resistive coating may include methods such as sputtering, evaporation, chemical vapor deposition, screen printing, or pad printing. The step of applying the insulative protective coating may include dip coating, meniscus coating, sputtering, evaporation, chemical vapor deposition, screen printing, or pad printing.
In one embodiment, the insulative protective coating is cured before the conductive edge electrode pattern is deposited thereon. Firing includes subjecting the panel to an elevated temperature via infrared radiation having a wavelength of between 2.5 and 6.0 microns.
In the preferred embodiment, a wire trace pattern is also deposited on the protective coating and the panel is fired until the wire trace pattern etches through the protective coating and makes electrical contact with the resistive coating. As such, the material of the wire trace pattern then includes conductive paste mixed with an additive. When the insulative protective coating includes silicon dioxide, the additive includes a chemical compound which is converted into a molten alkali hydroxide at elevated temperatures which dissolves the silicon dioxide of the protective coating.
The method may further include placing a wire trace pattern on the panel and providing electrical isolation between the wire traces and the edge electrodes. The method of providing electrical isolation may include incorporating a dielectric layer between the trace pattern and the protective coating. Electrical isolation may also be provided by incorporating a dielectric layer between the edge electrodes and the wire traces. Alternatively, by not adding an additive to the material at the wire traces, they do not etch through the protective coating and thus are electrically isolated from the edge electrodes.
This invention features a method of manufacturing a touch screen panel, the method comprising: applying a resistive coating to one surface of an insulative substrate, applying an insulative protective coating to the resistive coating, mixing a conductive paste with an additive, depositing the mixture in the form of a conductive edge electrode pattern including a plurality of edge electrodes on the protective coating, and firing the panel until the edge electrodes etch through the protective coating and make electrical contact with the resistive coating. The insulative protective coating usually includes silicon dioxide and the additive includes a chemical compound which is converted into a molten alkali hydroxide at elevated temperatures which dissolves the silicon dioxide of the protective coating. The chemical compound may be selected from the group consisting of sodium carbonates and/or sodium formates. The conductive paste may be a silver/frit composition. The additive typically comprises 1-25% by weight of the conductive paste.
In the preferred embodiment, the method further includes depositing a wire trace pattern on the protective coating and firing the panel until the wire trace pattern etches through the protective coating and makes electrical contact with the resistive coating. The material of the wire trace pattern includes conductive paste mixed with an additive. The insulative protective coating includes silicon dioxide and the additive includes a chemical compound which is converted into a molten alkali hydroxide at elevated temperatures which dissolves the silicon dioxide of the protective coating.
The method may further include the step of providing electrical isolation between the wire trace pattern and the edge electrodes. In one embodiment, a laser is used to etch the protective material and the resistive material between the edge electrodes and the wire traces.
This invention also features a touch screen panel comprising an insulative substrate; a resistive coating on one surface of the substrate; a protective coating on the resistive coating; and a conductive edge electrode pattern including a plurality of edge electrodes on the protective coating and extending to the resistive coating and making electrical contact therewith.
The panel may also include a wire trace pattern on the protective coating. A dielectric material may be disposed between the wire trace pattern and the protective coating. Alternatively, a dielectric material may be disposed over the conductive edge electrode pattern and then the wire trace pattern is on the dielectric material.